Sorry that this is almost a decade late, but for anyone that's still searching:

You can use domains to achieve this functionality

e.g.

<field name="job_id" domain="[('id', '=', -1)]"/>

Applying a domain that returns no results, as seen in the example, essentially forces the user to create a new record in order to select a value for this field.

Good luck!

Adding widget="selection" in xml against many2one field should solve your problem